Air compressors are becoming commonplace in home workshops. In general, an air compressor, or an air pump, is a machine that decreases the volume and increases the pressure of a quantity of air by mechanical means. Air thus compressed possesses great potential energy, because when the external pressure is removed, the air expands rapidly. The controlled expansive force of compressed air is used in many ways and provides the motive force for air motors and tools, including pneumatic hammers, air drills, sandblasting machines, and paint sprayers.
A conventional home workshop air compressor includes a storage tank for compressed air, and a prime mover mounted on the compressor tank for compressing the air flowing into the compressor tank. The prime mover may be a gas engine or an electric motor, but most conventional home workshop models utilize electric power. The compressor tanks are typically steel and cylindrical in shape, and sizes vary greatly, but typically, home workshop models range between four and thirty gallons. An air compressor typically includes a pedestal of some kind (e.g., four feet) that allows the compressor to rest on a surface such as a floor. Alternatively, for some larger models, a pair of wheels may be provided on one end of the compressor tank and a handle on the other end, permitting the air compressor to be wheeled around a work shop, for example.
In an air compressor, ambient air, which includes atmospheric humidity (i.e., water vapor), is drawn into the compressed air system where it is compressed to a desired discharge pressure. During the compression process, the water vapor is heated, and while stored in the compressor tank, the air and water vapor cool. Moisture, in the form of condensation, drops out of the airflow as it cools. This condensation accumulates in the bottom of the compressor tank, forming a liquid called a condensate.
Most home workshop air compressors include a drain at a lower portion of the compressor tank to drain condensate out of the compressor tank. The drain is typically a valve that extends into the compressor tank for the air compressor, and out beyond the sidewalls of the compressor tank.
Generally, an oilless air compressor (also termed an “air pump”) is an air compressor that utilizes a piston that does not require lubrication. One configuration of an oilless air compressor includes an electric motor rotating an eccentric which, in turn, causes a piston to reciprocate up and down within a cylinder. The eccentric translates the rotary motion of the motor into a reciprocating motion for the piston. On a piston down-stroke, air is pulled into the cylinder and on a piston up-stroke, air is compressed and forced out of the cylinder.
Air drawn into the cylinder of an oilless air compressor flows through one-way valves that permit the air to flow into the cylinder, but not flow out of the cylinder as the cylinder returns along an up-stroke. This air intake is often noisy, so many prior art air compressors include short pump head air intake mufflers. Although these air intake mufflers work well for their intended purpose, there is still quite a bit of noise from the intake valves that is audible to people in the air compressor's immediate surroundings.
The term “oilless” used to describe an air pump refers to the fact that a seal that wraps around the piston for the air pump and extends between the piston and the cylinder of the air pump is sufficiently resilient that it does not require oil to slide within the cylinder. The life of the seal is determined by the number of strokes, and the operating temperature to which the seal is subjected. To keep the operating temperature low, conventional air pumps often include cooling fans that direct a flow of ambient air over the cylinder, valve plate, and head.
The cylinder, valve plate, and head for an air pump are not the only parts that need to be cooled. The electric motor for an air pump also needs to be cooled. In addition, because the electric motor often rotates too fast to directly drive a piston, a drive belt is included that reduces the speed of rotation and provides a link between the electric motor and the piston. Because the operational life of this belt is determined by motor speed, motor torque, and belt temperature, the belt also needs to be cooled.
Most contemporary belt drive oilless air compressors utilize two separate fans: one for cooling the electric motor and its components, and the other for cooling the cylinder. An exception is the oilless air compressors disclosed in U.S. Pat. No. 5,137,434 to Wheeler, et al. Wheeler discloses an air compressor having a single fan mounted at one end of an air pump shroud that houses both the cylinder and the motor. Baffles are provided in the shroud to separate the air flow from the fan blades into first, second and third air flows. The first air flow passes sequentially over the motor commutator/brushes, between the rotors and stator and over the exterior walls of the cylinder. The second air flow is directed over the cylinder-head assembly, and the third air flow is directed over the drive belt. According to Wheeler, by splitting the air into different flow paths, the drive belt and the cylinder-head assembly are not subjected to heat from the motor.